1. Field of the Invention
The present invention relates to a quality control apparatus for controlling a manufacturing process and a control method of the same, a quality control program, and a recording medium recorded with the program for manufacturing products of predetermined quality.
2. Description of the Related Art
Traditionally, an effort to improve the quality of products is taken, and various quality control methods are proposed.
For example, in order to realize traceability, a management method is proposed in which identification codes such as bar codes are assigned to intermediate products for products and to bases on which the intermediate product is placed. Furthermore, in order to realize traceability, an identification method is proposed in which intermediate products are identified in order of the intermediate products to be put in each of manufacturing process steps.
Moreover, a method is proposed in which the cause-and-effect relationship between controllable factors and product characteristics is fully comprehended to specify the controllable factors for obtaining optimum product characteristics. Besides, a method is proposed in which the entire conditions of controllable factors are fixed to maintain product characteristics (for example, see Patent Documents 2 and 3).
In addition, a method is proposed in which indicators for individual product characteristics are provided to do comprehensive evaluation from these indicators. Furthermore, a method is proposed in which it is determined whether product characteristics is passed or failed at the final process step in production and controlled parameters are adjusted in manufacturing process steps when a product is determined as a defective (for example, see Patent Document 1).    Patent Document 1: JP-A-7-141005 (published on Jun. 2, 1995)    Patent Document 2: JP-A-6-110504 (published on Apr. 22, 1994)    Patent Document 3: JP-A-4-188301 (published on Jul. 6, 1992)    Non-patent Document 1: TAGUCHI Gen'ichi, and YOSHIZAWA Masataka, Hinshitsu Kogaku Koza 1/Kaihatsu-Sekkie Dankai no Hinshitsu Kogaku, Nihon Kikaku Kyokai, 1988
However, in the method that assigns the identification code for management, there is a problem that production costs are increased. Furthermore, defectives are often drawn, reworked, and put back in manufacturing process steps. On this account, the method that identifies the intermediate products in order of the intermediate products does not always identify the intermediate products correctly.
Moreover, since many controllable factors exist, many verification experiments are required to fully comprehend the cause-and-effect relationship between the controllable factors and the product characteristics. Besides, the more complicated the cause-and-effect relationship is, the more difficult the full comprehension is. Furthermore, even though all the conditions of the controllable factors are fixed, an unobservable change in factors over time can varies the product characteristics.
Moreover, in the method that performs comprehensive evaluation from the indicators for the individual product characteristics, since the product characteristics often have a trade-off relationship each other, it is difficult to perform comprehensive evaluation. Besides, in the method that determines whether the product characteristics are passed or failed at the final process step in production, defectives are continuously fabricated until the final process step, and thus unnecessary production time and materials are increased. Furthermore, the intervals between control feedback loops are also increased.